The present invention is utilized in suppressed carrier communications systems and particularly in multiplex systems where a plurality of systems utilizing pilot signals of different frequencies may be connected together. Also, in many instances, it may be desirable to transfer equipment from one system using a first frequency pilot signal to a second system using a different frequency pilot signal.
In the prior art, equipment has always been manufactured for use with a single pilot signal and, if the equipment is to be used with a different frequency pilot signal, it had to be returned to the factory where crystals and filters were changed and the equipment rewired to receive the different frequency pilot signal. Returning units to the factory for conversion of the pilot signal is extremely expensive and time consuming. Also, the system, or at least portions thereof, is inoperative while the units are being converted.